Laser welding apparatuses are included in the application fields of laser processing. In laser welding, a plasma, which considerably affects the behavior of the molten value, is generated during the process. Accordingly, shield gas is generally blown during the welding to remove the plasma. Furthermore, because fume and sputters adhere to the nozzle to impair the optical system, measures for preventing them from forming have also been studied.
Shield gas blowing can be carried out by either a center gas type process or a side gas type process.
In the center gas type process, as illustrated in FIG. 24, the gas is blown co-axially with the laser beam. This process is mostly used for laser cutting (for example published JP58-2754 and JP59-37159).
In the side gas type process, on the other hand, a gas is blown to the weld through a path other than the laser beam as shown in FIG. 25. This type of gas blowing is carried out using a side nozzle, and is utilized for suppressing the plasma and for improving the welding bead (for example published JP60-32556 and laid opened JP58-168490).
There are also cases in which ring-shaped nozzles are used. Such nozzles are used for concentrating the shield gas, as disclosed in, for example, JP56-151191(laid opened), or for preventing the adhesion of metal melt during cutting, as disclosed, for example, JP03-23275(published).
Useful as the shield gas include gases of rare elements such as Ar, He, Xe, Kr, and Ne; inert gases such as N.sub.2 ; and reactive gases such as CO.sub.2 and H.sub.2 ; as well as the gases obtained by mixing two or more gases selected therefrom.
The processes described above, however, suffer problems as follows.
(1) Clogging occurs on the nozzle top, due to the scattered sputter and metal vapor which generate on the welding workpiece;
(2) Bead characteristics in some materials such as aluminum is impaired, because a metal oxide (inclusive of those having a composition deviating from stoichiometry) which generates from the work on laser irradiation to the surface of the workpiece adheres to the bead;
(3) Directivity along the nozzle direction (gas blowing direction) is observed with respect to the direction of laser scanning (welding direction);
(4) Defective bead appearance such as undercuts and humping results under an excessive supply of shield gas which blows down the molten value; materials of low melt viscosity are more apt to suffer this problem;
(5) Unsound solidification structures result under an insufficient amount of shield gas, due to the oxidation of the metal; and
(6) Under a favorable blowing of shield gas, the weld depth (penetration) falls at a constant value; otherwise, the weld depth is reduced.
In practicing laser welding, however, the problems above are found to occur concomitantly with each other. Accordingly, it is keenly desired to establish an industrially feasible gas shielding process which overcomes all of the problems enumerated above.
A laser processing process which comprises blowing an inert gas against the laser irradiated portion through a ring-shaped nozzle is disclosed in JP56-151191(laid opened) referred herein before (see FIGS. 2 and 4 attached thereto). In this process, however, no consideration is made on the angle between the inner and the outer nozzles and on the positional relation between the nozzles and the workpiece. Accordingly, the problems (1) to (6) as enumerated above remain yet to be solved.
Similarly, the same problems remain unsolved in the process disclosed in JP03-23275(published).
An object of the present invention is to provide a laser irradiation nozzle free from at least one of the problems above; and a laser irradiation nozzle in which the nozzle clogging is prevented from occurring, in which the adhesion of metal oxides is prevented, which enables a non-directional gas blowing, which provides sound bead morphology, which prevents oxidation from occurring on the weld, and which provides a stable penetration depth of the work.